Welcome to the frustrating world of "finding Comanche specific parts"! The rear bumper is especially hard because of the funky mounting design. All is not lost though, several options do exist.
-Stock style replacement:
http://jcwhitney.com/item.jhtml?ITEMID=10435
-Tube bumper style (with reciever hitch):
http://www.genuinesteel.com/
(you'll need to call them to find a local dealer)
-Build your own!
This is the most common method for obvious reasons. Creativity is your friend! Here are some examples:
Mine:
I don't have access to cool metal-working machinery, so I went with more of a cheap/easy route. I had to sacrifice use of my tailgate though with my particular design. More pics (including how I built it) are at the project page in my signature. MAybe it'll give you some ideas for your own.
Terry's (cjatheart):
A simpler design incoperating the stock bumper brackets. Variations on this idea could include a reciever hitch.
And my favorite, custom made by Boulderbars:
http://www.boulderbars.com/custom.htm
This one utilizes a drop in the bracket so the functionality of the tailgate is retained. It also incorporates the upper shackle bolt for more strength. I really, really like it, but you'll need to call them to see if they can make you one too.
Jeep on!
--Pete